The present invention relates generally to semiconductor integrated circuits (ICs). In particular, the invention relates to reducing the size of sense amplifiers used in ICs such as memory ICs.
Semiconductor ICs, such as memory ICs, employ sense amplifiers, for example, to read, write, and restore information in the memory cells. A sense amplifier is provided for a bitline pair of the memory IC. During operation, the sense amplifier senses and amplifies a differential voltage between the bitlines of the bitline pair. The differential voltage indicates whether the charge stored in the selected memory cell is a logic 1 or logic 0.
A continuing demand for higher integration and lower manufacturing cost has placed increasing pressures on IC manufacturers to produce smaller and smaller chips. Since the sense amplifiers, in a typical memory IC, contribute to about 10% of the chip size, decreasing the size of a sense amplifier can provide a noticeable reduction in the overall chip size.
Generally, a sense amplifier includes cross-coupled latches for sensing the differential voltage between the bitline pair. The sense amplifier also includes drivers for driving the latches in order to amplify the sensed differential voltage. The drivers are relatively large and contribute significantly to the size of the sense amplifier.
Reducing the size of the drivers can noticeably reduce the size of the sense amplifier. However, the drivers require a minimum dimension due to design requirements. Reducing the size of the drivers to smaller than the minimum dimension can result in a decrease in the performance of the drivers, which adversely impacts the performance or the functionality of the IC.
One technique of reducing the size of the sense amplifier is to locate the drivers outside of the general sense amplifier region. For example, the drivers can be located in the stitch gap region between sense amplifiers of a stitched wordline architecture or in the local wordline driver region between the sense amplifiers in a segmented wordline architecture. Other areas in which the drivers can be located include the row decoder region. However, smaller groundrules have decreased the surface area of the stitch gap or local wordline driver region, making it difficult to accommodate the drivers.
As evidenced from the foregoing discussion, it is desirable to decrease the size of sense amplifiers without decreasing their performance or affecting their functionality.
The invention relates to reducing the size of sense amplifiers. In one embodiment, an active input signal which activates the driver of the sense amplifier produces an increase in the overdrive voltage to cause the driver to operate in the increased overdrive mode. This enables the use of a smaller driver which facilitates a more efficient layout and/or reduces the size of the sense amplifiers.